The invention addresses the field of mobile communications. The invention relates to a method for protecting against overload of a multipoint-to-point channel of a mobile communication network, the multipoint-to-point channel being provided by a radio access network for the mobile communication network in order to enable a plurality of mobile communication means to access the mobile communication network, wherein each mobile communication means can attach to the multipoint-to-point channel to provide processing requests of at least two different request types through the multipoint-to-point channel to the mobile communication network, in particular to a packet switching node of the mobile communication network. The invention further relates to a network node element of a communication network, a communication network, a computer program, and a machine-readable medium.
A system for mobile communications is known that comprises a first cellular network according to the Japanese “Personal Digital Cellular” (PDC) standard, also called “Pacific Digital Cellular” standard, that is based on the known RCR-STD 27 standard, version H, of the Association of Radio Industries and Businesses (ARIB), and a second cellular network according to the “Packet Personal Digital Cellular” (PPDC) standard, also called “Packet Pacific Digital Cellular” standard.
The Packet Personal Digital Cellular network comprises a packet mobile services switching center (PMSC) that realizes a switching of packet data exchanged between a mobile station of a subscriber and, for example, an application server holding packet data content for the subscriber.
The Packet Personal Digital Cellular network comprises a radio access network with a base station in each cell of the cellular network, wherein the base stations include a transceiver and an antenna for communication over the air with the mobile station located in the cell. The cellular network provides a packet communication physical channel (PPCH) between the mobile station and the base station. This physical channel is a particular dedicated Radio Frequency Time Slot (RFTS) within a Time Division Multiple Access (TDMA) frame structure on a carrier frequency. Radio signals transmitted from and received by the base station are used by the mobile station to communicate with the network via the packet communication physical channel. The base station provides the packet data received in the radio signals from the mobile station to the packet mobile services switching center. A user packet channel (UPCH) is used as a logical channel between the mobile station and the packet mobile services switching center in order to transmit the packet data from the mobile station to the packet mobile services switching center. The logical channel used for carrying user packet data, i.e., the user packet channel, is defined as a particular Radio Frequency Time Slot (RFTS) of the packet communication physical channel (PPCH).
The user packet channel is a point-to-multipoint bi-directional channel, for example, used in cellular 2G+ (Second Generation Plus) networks to transfer user packet data and the corresponding control signals between the base station and the connected mobile stations. The bandwidth of the user packet channel is shared between all mobile stations which are currently connected to the channel. Data traffic in downlink (also called: downstream) direction, i.e. from the network to the mobile station, is controlled by the base station. The base station determines when to send which data packet. Thus, access control to the channel is concentrated in one single instance, such that on the channel, in downlink direction, no two packets are sent out at the same time.
Compared with the well-regulated data traffic on the user packet channel in the downlink direction, in the uplink (also called: upstream) direction, i.e. in the direction from the mobile station to the network, in particular to the packet mobile services switching center, a plurality of independent mobile stations located in the cell of the base station randomly compete for access to the same resource, that is the same channel is shared by the mobile stations. The competition is thus organized in a random access mode. As a result, the throughput of data packets through the user packet channel depends on the number of data packets which are offered for transfer over the channel.
The relation between offered data packets and throughput of data packets is shown in FIG. 1. As the number of offered data packets is raised, the throughput of data packets first rises up to a number of data packets t(opt) where approximately twenty percent of the theoretical capacity of the user packet channel is used for throughput of data packets. However, as the number of offered data packets is further raised, instead of a further increase in throughput of data packets, despite the unused theoretical capacity of the channel, the throughput of data packets decreases below t(opt). Thus, throughput through the user packet channel reaches an early optimum at an optimum number o(opt) of offered data packets before degrading. To the left of the optimum number o(opt), the throughput of data packets cannot be raised because there is nothing more to transfer. However, to the right of the optimum number o(opt) of offered data packets, there is too much transfer of data packets resulting in a growing number of packet collisions. Packets being sent out simultaneously from different mobile stations interfere in the air and destroy each other such that a retransmission is required. The retransmission of those data packets costs bandwidth. Of course, the retransmission can fail such that a further retransmission is required.
As a result, once the offered data packet traffic exceeds the limit of the optimum number o(opt) of offered data packets, uplink packet data traffic from the mobile stations visiting a cell to the packet mobile services switching center that controls this cell provides an unstable system: retransmissions of some offered data packets will be necessary that add to the offered traffic such that even more retransmissions are required adding further to the offered traffic—until the system collapses, i.e. until the channel is congested.
A call admission control (CAC) system has been proposed to protect the user packet channel against overload such that the optimum number o(opt) of offered data packets is not exceeded. Thus the channel should be kept usable for the users registered to the packet mobile services switching center. The known call admission control system uses complex algorithms to prevent the overload situation. Approaches were proposed to model a network behavior based on queuing of handover requests and queuing of new call arrivals sent by a mobile station. Requirements of the call admission control mechanism are summarized for the mechanism to be implemented in the base station. However, the known call admission control system is disadvantageous for the following reasons: regarding processing time and memory, queuing of new call arrivals and queuing of handover requests are cost intensive operations and, regarding timing, they lead to a delay of a response to the requesting mobile station. Moreover, the base station only obtains fragments of the information related to new call arrivals and handover requests and therefore does not know about new call arrivals or handover requests outside its coverage area.
The problem underlying the invention is to enable a protection against overload that is efficient and simple to run while requiring few system resources such that the system quality of service to users is improved.